The present invention is directed generally toward friction stir welding and, more particularly, toward an improved tool for use in friction stir welding processes.
Friction stir welding is a process that makes use of frictional heat, which includes the heat generated between a rotating, non-consumable pin and workpieces and the heat generated as a result of plastic work from the workpiece material being strained and mixed, to weld the workpieces together. The produced frictional heat plasticizes the workpiece materials and consolidates them to create one piece of material where there were originally two. Friction stir welding is used for joining together various parts of materials, such as metals, plastics, and other materials that will soften and consolidate under applied frictional heat to become integrally connected. While friction stir welding has been commonly applied to butt joints and corner joints, it can also be applied to lap joints and other types of joints, as well as for eliminating or closing cracks in a given material and for joining together two sides of a material to form a hollow section, such as a tube.
A prior art apparatus for friction stir welding is shown generally in FIG. 1. The apparatus 10 is rotatable about an axis 12, and includes a support body 14 and a non-consumable pin 16 extending from a distal end of the support body 14. As shown in FIG. 1, two workpieces 18 and 20 are aligned so that the edges of the workpieces to be welded together are held in direct contact at an interface 22. As the rotating apparatus 10 is brought into contact with the interface 22 between the workpieces 18 and 20, the rotating pin 16 is forced into contact with the material of both workpieces 18 and 20, as shown in FIG. 1. The pin 16 is inserted into the material of the workpieces 18 and 20 until a flat shoulder 24 at the distal end of the support body 14 contacts the upper surface of the workpieces 18 and 20. As the apparatus 10 is moved through the material, the rotation of the pin 16 in the material and the rubbing of the flat shoulder 24 against the upper surface of the workpieces 18 and 20, as well as the resultant plastic work from the workpiece material being strained and mixed, produces a large amount of frictional heat in the vicinity of the workpiece interface 22. This frictional heat softens the material of the workpieces 18 and 20 in the vicinity of the rotating pin 16 and shoulder 24 creating a plasticized region and causing commingling of the material which, upon hardening, forms a weld 26. As the apparatus 10 is moved longitudinally along the interface 22, the weld 26 is formed along the interface 22 between the workpieces 18 and 20, thereby joining the workpieces 18 and 20 together. The flat shoulder 24 of the support body 14 prevents softened material from the workpieces from escaping upward, and forces the material into the plasticized region. When the weld is completed, the apparatus 10 is removed.
Prior art friction stir welding tools require minimal differences in workpiece thickness across the weld joint. Thus, fluctuations in the thickness of the workpieces at their interface may compromise the integrity of the weld formed by friction stir welding processes. Similarly, prior art friction stir welding tools require that the position of the tool be precisely controlled relative to the upper surface of the workpieces in order to generate sufficient frictional heat to adequately plasticize the material. Failure to generate sufficient frictional heat will also compromise the integrity of the weld joint.
Additionally, for prior art bobbin-type friction stir welding tools, the pin and back shoulder must be precisely controlled relative to the back surface of the workpieces. Thus, the pin must be independently movable axially relative to the front shoulder, e.g., support body 14, of the friction stir welding tool.
The present invention is directed toward overcoming one or more of the above-mentioned problems.
A friction stir welding tool is provided, according to the present invention, for joining together workpieces utilizing friction stir welding processes. The inventive tool includes a support body rotatable about a first axis and having a distal end defining a shoulder. A rotatable pin extends from the distal end of the support body downward from the shoulder. The shoulder of the support body includes at least one section that is tapered, with the taper extending downward toward the pin.
In one form of the present invention, the shoulder includes a face having at least one groove formed therein. The at least one groove may include either a spiral formed groove or a plurality of concentric grooves formed in the face of the shoulder.
In another form of the present invention, the shoulder includes a substantially flat section and a tapered section having a taper extending downward toward the pin. The substantially flat and tapered sections are concentric and displaced radially from the pin to the outer edge of the support body. Preferably, the substantially flat section is provided adjacent the pin, and the tapered section is provided adjacent the outer edge of the support body. However, an opposite arrangement of the sections may be utilized.
In yet another form of the present invention, the shoulder includes first and second tapered sections. The first tapered section has a first taper extending downward toward the pin. The first taper is formed at a first angle referenced from a plane perpendicular to the first axis. The second tapered section has a second taper also extending downward toward the pin. The second taper is formed at a second angle, greater than the first angle, referenced from a plane perpendicular to the first axis. The first and second tapered sections are concentric and displaced radially from the pin to the outer edge of the support body. Preferably, the first tapered section is provided adjacent the pin, and the second tapered section is provided adjacent the outer edge of the support body. However, an opposite arrangement of the sections may be utilized.
In still another form of the present invention, the shoulder additionally includes a third tapered section having a third taper extending downward toward the pin. The third taper is formed at a third angle, different than the first and second angles, referenced from a plane perpendicular to the first axis. The first, second and third tapered sections are concentric and displaced radially from the pin to the outer edge of the support body. Preferably, the second angle is greater than both the first and third angles, with the first tapered section provided adjacent the pin, the third tapered portion provided adjacent the outer edge of the support body, and the second tapered section provided between the first and third tapered sections However, alternate arrangements of the sections may be utilized.
The third angle may be greater than or equal the first angle. In a further form of the present invention, the first angle is substantially 0xc2x0, such that the first tapered portion is substantially flat.
In an additional form of the present invention, each of the first, second, and third tapered sections includes a face having at least one groove formed therein. The at least one groove formed in each of the first, second and third section faces may include either a spiral formed groove or a plurality of concentric grooves. In one form, the grooves are formed normal to the respective planes of the first, second and third section faces.
In an alternate embodiment of the present invention, the friction stir welding tool further includes a bottom support member connected to a distal end of the pin, such that the pin is disposed between the support body and the bottom support member. In this embodiment, the inventive tool is configured as a bobbin-type friction stir welding tool. The bottom support member is also rotatable about the first axis and includes a bottom shoulder facing the shoulder of the support body. The bottom shoulder of the bottom support member includes at least one portion that is tapered, with the taper extending upward toward the pin.
In one form of the alternate embodiment, the tapering is such that the shoulder of the support body and the bottom shoulder of the bottom support member are formed as mirror images of one another.
In another form of the alternate embodiment, the bottom shoulder includes a face having at least one groove formed therein. The at least one groove may include either a spiral formed groove or a plurality of concentric grooves formed in the face of the bottom shoulder.
With the inventive tool configured as a bobbin-type welding tool, the support body, pin and bottom support member may be integrally formed, or connected via conventional connection means.
It is an object of the present invention to provide a friction stir welding tool having an improved tolerance to joint mismatch at the interface of the workpieces to be joined.
It is a further object of the present invention to provide a friction stir welding tool having increased heat generation properties.
It is yet a further object of the present invention to provide a friction stir welding tool having robust operational properties of the welding process.
It is still a further object of the present invention to provide a friction stir welding tool capable of facilitating fixed-pin bobbin-type welds.
Other objects, aspects and advantages of the present invention can be obtained from a study of the specification, the drawings, and the appended claims.